Spectroscopic imaging combines digital imaging and molecular spectroscopy techniques, which can include Raman scattering, fluorescence, photoluminescence, ultraviolet, visible and infrared absorption spectroscopies. When applied to the chemical analysis of materials, spectroscopic imaging is commonly referred to as chemical imaging. Instruments for performing spectroscopic (i.e. chemical) imaging typically comprise image gathering optics, focal plane array imaging detectors and imaging spectrometers.
In general, the sample size determines the choice of image gathering optic. For example, a microscope is typically employed for the analysis of sub micron to millimeter spatial dimension samples. For larger objects, in the range of millimeter to meter dimensions, macro lens optics are appropriate. For samples located within relatively inaccessible environments, flexible fiberscopes or rigid borescopes can be employed. For very large scale objects, such as planetary objects, telescopes are appropriate image gathering optics.
Regardless of the type of optical equipment, a first step in any spectroscopic investigation is defining a suitable wavelength for illuminating the sample. The step of defining an suitable wavelength for illuminating the sample becomes even more important when simultaneous multiple images of the sample are sought. Conventional methods suggest illuminating a sample with a first wavelengths (e.g., NIR or VIS) to obtain a first image, followed by illuminating the sample with a second wavelengths to obtain a second image (e.g., Raman or dispersive Raman) to obtain a second image. Consequently, the conventional process are time consuming and are not suited for simultaneous imaging of the ample. There is a need for a apparatus and method for determining illumination parameters of a sample a priori of illuminating the sample.